well you wouldn't use ssh *and* scp together, as they are the same thing inside....
ok. start again....
you use ssh to get into your lan and then want to copy files across that conenction and directly into another machine in your private network? ok that's fine... as part of your ssh connection, add a tunnel, e.g. -L 1234
thermachinesip:22 and log in. then you can launch scp to connect to 127.0.0.1:1234. connecting to that will actually connect to othermachinesip:22 i.e. ssh/scp/sftp on the "unreachable" machine. that what you mean?